I guess my answer would depend on how attached you are to these UFO's.... If not too attached, find a quick-finish method and send to local shelters, clothing banks, etc.
If you're attached, finish and share with people you love who would appreciate them.
As far as storage of UFO's... I guess I'm fortunate, there really aren't any UFO's that hang around here. There's the random pieces where I tried something new, but I even try to finish them, even if it's a pillow for the kids. Unless it's really awful, then the trash can is a good place.